1. Field of the Invention
This invention relates to an optical apparatus, and a displacement-information measuring apparatus using that apparatus. The invention is suitable as an optical displacement sensor, such as an encoder, a speed sensor, an acceleration sensor or the like, for measuring the displacement or speed of a moving object. The invention utilizes the phenomenon that when a light beam that is projected onto an object is diffracted or scattered, the phase of the diffracted or scattered light beam is modulated in accordance with the displacement or speed of the object.
2. Description of the Related Art
Displacement measuring apparatuses, such as optical encoders, laser Doppler velocimeters, laser interferometers and the like, for obtaining a physical quantity, such as the displacement or speed of an object, with high precision by projecting light onto the object and detecting the light beam from the object have been widely utilized mainly in the field of NC (numerical control) machine tools, OA (office automation) apparatuses, robots and the like.
As examples of such displacement measuring apparatuses, optical encoders have been disclosed in Japanese Utility Model Laid-open Application (Kokai) No. 1-180615 (1989) and Japanese Patent Laid-open Application (Kokai) No. 62-121314 (1987).
In order to measure relative displacement information of a moving object with high precision, it is necessary to set the relative optical positional relationship among respective components, such as a light-emitting device, a condenser lens, diffraction gratings, photosensors and the like, which constitute a displacement measuring apparatus, with high precision.